The present invention relates to a method for coordinating braking forces between two connected units forming a vehicle train.
A method for providing coordination of braking forces in connected units of a vehicle train is disclosed for example in EP 0 532 863 B1 (U.S. Pat. No. 5,333,940). The method disclosed therein is directed to use with a towing vehicle and a trailer which together constitute two connected units in a vehicle train subjectable to independent braking forces. The known method attempts to obtain even distribution of braking force through adaptive influence exerted upon the trailer braking pressure which generates the braking force in the trailer controlled from the towing vehicle.
Control of the trailer braking pressure is based upon slip-encumbered wheel speed signals which are obtained from wheels on both units of the vehicle train and transmitted for central evaluation within the towing vehicle as speed signals corresponding to a particular unit of the vehicle train.
The different braking forces on the slipping wheels, analysis of which provides a basis for adaptively influencing the trailer braking pressure, are assumed by applying a physical law relating braking force and a difference between the various measured slip-encumbered wheel signals. In accordance with the known method, the braking pressure of the trailer is adaptively influenced when a difference is detected between the speed signals of the various wheels of a unit or between the speed signals of the towing vehicle and the trailer calculated from same, in such manner that the difference between the speed signals is minimized, and braking forces are thereby divided nearly equally between the towing vehicle and the trailer.
The above described method requires that at least one speed signal from each unit of the vehicle train, i.e. the towing vehicle and the trailer, be transmitted to an electronic control device which centrally evaluates the speed signals and effects adaptive influence of the trailer braking pressure to properly coordinate the braking forces.
Since the vehicle train may at times be very large, a substantial time offset may occur between the speed signals, caused for example by running times during signal transmission from the trailer to the towing vehicle, or due to different filtering processes of the wheel speed signals in the units of the vehicle train.
As a consequence, practice of the known method may at times result in insufficient coordination of the braking forces between the towing vehicle and the trailer, resulting in unequal brake lining wear for different wheels, extended braking distance and, under certain conditions, hazardous braking.
It is therefore an object of the invention to provide a method for the coordination of braking forces between two connected units which comprise a vehicle train, in which precise control is made possible even when speed signals of different kinds are used.